It is known that when scoring or cutting (collectively herein cutting) wallboard materials such as gypsum board, wallboard, plasterboard, insulation board, or like materials particularly in construction applications that time to perform cutting operations can be reduced and quality of cut increased when using cutting tools referenced to an edge of the wallboard material as in the case of a T-Square guided knife. Cutting of wallboard needs to be quite accurate in most cases as the material is often used in finishing interiors of buildings where fit ultimately affects the quality and appearance of the finish. Furthermore the cutting of wallboard materials should be quick and easy to maximize installer productivity and reduce overall cost of installation.
In most cases, wallboard materials can be cut by first scoring the surface, and then bending the board along the score line so as to break the board. Scoring a long line of 4 feet, typical gypsum board width, or even longer lines of 8 to 12 feet or more can be difficult without a referenced guide. Long straight edges often get bent and malformed due to miss-handling during the course of normal construction work and transportation between job sites. Several attempts aimed at resolving this challenge have been made as shown in U.S. Pat. No. 6,629,370 issued to Sposato on Oct. 7, 2003, which teaches of a board cutter including a T-Square and a common utility knife mounted to a slider which rides along the long leg of the T-Square and is fixed at a position by means of a clamp mechanism as in a thumb screw. The common utility knife is connected to the slider by way of a pivotal pin, and clamped into a depth of cut position again using a thumb screw arrangement. The primary drawback of the Sposato patent is that is difficult to cut the full face of a wallboard from edge to edge as the T-Square runs out before the knife has scored the whole length of the surface. This is particularly evident when cutting a wallboard while it is standing on end as when leaning against a wall, the leading end of the head of the T-Square is blocked by the floor or ceiling preventing the knife from reaching the edges closest to the obstructing floor or ceiling. These draw-backs are addressed in my U.S. Pat. No. 7,178,246 which issued Feb. 20, 2007, entitled Wallboard Cutting Tool, and is incorporated herein by reference.
A further drawback of prior art utility knives or wallboard cutting knives is the difficulty in changing or reversing the cutting blades in the knife. It is an object of the present invention to provide an improved mechanism for holding and releasing such blades in utility knives or the like. In the prior art applicant is aware of United States Patent Publication No. US2007/0157472, published Jul. 12, 2007.